A hybrid vehicle comprises an internal combustion engine, which transmits the torque to the drive wheels by means of a transmission provided with a gearbox, and at least one electric motor which is electrically connected to an electric storage system and is mechanically connected to the drive wheels.
In order to increase the overall energy efficiency during all steps of decelerating, the electric motor may be used as a generator for effecting a regenerative deceleration in which the kinetic energy possessed by the vehicle instead of being completely dissipated into heat generated by friction, is partially converted into electricity which is stored in the electric storage system. For this purpose, when the driver presses the brake pedal, a control unit of the braking system does not initially operate the mechanical brakes and pilots the electric motor as a generator, so that the braking torque is generated only by the electric motor; if the driver presses the brake pedal in a more vigorous manner thus requiring a high braking torque which is higher than the capacity of the electric motor, the control unit of the braking system also operates the mechanical brakes.
In the currently marketed traditional braking systems, the mechanical brakes are hydraulically piloted and the brake pedal directly acts on a brake pump which raises the pressure in a braking circuit with the aid of a servo brake system In order to implement the above-described regenerative braking mode, it has been suggested to suppress the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit; in this case, the position of the brake pedal is detected by a position sensor and according to the brake pedal position read by the position sensor, the control unit of the braking system pilots the electric motor as a generator and, if needed, also operates the mechanical brakes using an actuator (e.g. an electric actuator) coupled to the brake pump which raises the pressure in the braking circuit.
Suppressing the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit results, however, in fully redesigning the braking system and thus high costs and long manufacturing times. Furthermore, suppressing the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit makes it difficult to operate the brakes in case of errors or malfunctioning of the position sensor which reads the position of the brake pedal or in the actuator coupled to the brake pump; therefore, adequate redundancies and adequate diagnostics should be provided to ensure a high degree of vehicle driving safety.
Patent applications WO2005014351A1 and WO2005102804A1, which are incorporated by reference, describe a braking system for a vehicle to control a regenerative braking; the braking system is provided with: a plurality of hydraulically operated mechanical brakes; a hydraulic braking circuit connected to the mechanical brakes; a brake pump to raise pressure in the hydraulic braking circuit; a brake pedal mobile between a resting position and a maximal braking position; a connecting cap, which mechanically connects the brake pedal to the brake pump, and is divided into two reciprocally independent parts; an elastic system which tends to push the brake pedal towards the resting position; a position sensor to read the position of a part of the connecting cap integral to the brake pedal; and a pilot system to pilot an energy recovery system for effecting a regenerative braking using the position of the part of the connecting cap integral to the brake pedal provided by the position sensor The mechanical solution used in patent applications WO2005014351A1 and WO2005102804A1 for implementing the elastic system tending to push the brake pedal towards the resting position is, however, particularly complex and expensive.